This invention is generally related to the field of repetitive batch weighing of products either as a step in their packaging for sale or use, or for use in mixing of products. More particularly, the invention relates to a batch weighing system and associated scales that provides improved accuracy and simultaneously increases the speed of the packaging or weighment of the product.
The packaging of foods and other household products has increased many orders of magnitude within the past few years both as to the number of applications and as to the quantity of packages produced in each application. With this increase in quantity the packaging machinery has grown steadily more sophisticated and faster but the pace of these improvements has often been slowed by the one common denominator of all various methods and apparatus employed, the need to accurately weigh the product being packaged.
There have been many improvements in weighing devices such as that disclosed in U.S. Pat. No. 3,802,522. The batch weighing system disclosed in the above-mentioned patent produces a very accurate and fast weightment by achieving a critical scale damping factor in the weighing system. While this has proven to be very successful, the systems of this type may generally be stated to have a flaw in that in order to achieve the critical scale damping factor the first excursion of the scale voltage which passes the target weighment voltage is used to trigger the cessation of the weighment process. Such a decision is an irreversible decision and, in the case of scale overshoot, can lead to under weighment.
Automatic scale systems as known in the prior art have utilized the vernier weighment principle. In a vernier system, material is delivered to a scale at an initial high volume feed rate with limited accuracy to a weighment somewhat less than the final weighment desired. Then a much slower, or dribbling, feed rate is used to bring the weight up to the final weighment required. However, as the final weight is approached the scale damping, due to the possibility of overshoot of the scale used for the weighment, becomes a crucial factor. In the previously mentioned patent, the weighment system triggered feed stop on its initial excursion past a target weighment voltage. The weighment was assumed to be complete at this point, and the dump cycle of the apparatus was initiated. This places a high accuracy requirement on the achievement of critical damping factor in the scale mechanical and electrical componentry. In the present invention, however, improved circuitry is included to ensure that in fact the weighment process is actually complete and that a scale overshoot is not causing premature initiation of the dumping cycle to take place. Thus, critical damping in the mechanical and electrical components, while still highly desirable, is not crucial.
Additionally, in the present invention a novel and more accurate means for delivering the preliminary bulk targeting weight of feed material to the vernier feeding plan is achieved by the use of a bulking servo system. In this system, comparisons of the actual bulk delivery and a bluk target weight are made and the system delivering the bulk quantity is adjusted in its feed rate to more closely approximate the desired bulking characteristic. This leads to more rapid filling of the weighment scale.
Accordingly, it is an object of the present invention to provide a more accurate and faster bulk weighment system than has heretofore been available.
Another object of the present invention is to provide a vernier type bulk weighment system in which achieving a critical damping factor of the scale weighment apparatus does not constitute a crucial factor in the system.
Yet another object of the present invention is to provide a bulk weighment system of the vernier type wherein a bulk quantity of product delivered in the initial portion of the operation cycle of the apparatus is controlled in response to the performance of the prior attempts of the apparatus to deliver a correct target bulk amount.